The present invention relates to an electropneumatic device for the automatic and complete threading of apparatuses for feeding weft to textile machines and to a weft feeding apparatus which includes said device.
As is known, weft feeders are apparatuses which are suitable to draw the weft thread from spools, to accumulate a reserve of weft in the form of turns of thread wound around a fixed drum and to feed said thread to the textile machine, for example a gripper or bullet loom, with a controlled and constant tension and in an amount linked to the demand of the machine itself.
For this purpose, weft feeders comprise, according to a known arrangement, a fixed drum at the base of which a ring is rotatably arranged; said ring is provided with a radial or substantially radial hollow arm in which the thread runs and, by virtue of the rotation of the ring, winds on drum, forming the turns of the weft reserve. The thread reaches the cavity of the radial arm by passing in a similar cavity of the drive shaft of the disk and unwinds from the drum by passing through a braking means which is in elastic contact with the drum and with a terminal thread guiding ring which is arranged coaxially to said drum; ceramic inlet, intermediate and outlet bushes are provided respectively at the inlet of the drive shaft of the ring, at the outlet of the hollow radial arm and on said terminal thread guide.
When the spool located upstream of the pre-feeder ends, or when the thread breaks, the weft reserve is correspondingly depleted and it is necessary to rethread the feeder. Due to the convoluted shape of the path of the thread, and especially to the obstacle constituted by the braking means, the threading operation is performed manually, at least in the front part of the apparatus which is comprised between the intermediate bush and the outlet bush by using a tool, commonly termed "drawboy", which consists of a flexible metallic wire which can follow the path of the thread and at the head of which there is an eye or another means for connecting the thread.
In practice, the drawboy is inserted in the pre-feeder, from the front side, through the bush of the thread guide and the braking means, and then the thread is connected to the head of the drawboy; by pulling back the drawboy from the front side, the thread is fully threaded in the pre-feeder; the threading of the rear part of the apparatus, comprised between the inlet bush and the intermediate bush, is performed in a known manner by means of a pressurized pneumatic fluid.
The use of the drawboy is quite onerous, requires considerable specialization on the part of the operator but, most of all requires a considerable time for execution, which negatively affects the efficiency of the loom or textile machine.
The prior international application WO 89/02944 already described a device which eliminates the use of the drawboy by performing automatic threading in the front part of the apparatus by means of a wall of pressurized fluid, generated by annular nozzles and/or by tubular ducts, which passes through the braking means. The described arrangement assumes, however, that the braking means surrounds the drum so that there is a free annular gap between said braking means and said drum, as in the case of FIG. 1 of said application, or an annular gap affected by a ring of bristles, as in the case of FIG. 2 of the same application.
However, this known arrangement is unsuitable to produce threading through a continuous braking means which frontally and elastically adheres to the drum of the apparatus, for example a braking means of the kind described in U.S. Pat. No. 5,316,051 in the name of the same Applicants, since such a braking means interacts with the wall of fluid and with the thread entrained it, preventing its transit.